Monthly income physiotherapist

Daily receipts can be filled in on a daily basis.
https://dexxter.be/wat-is-een-dagontvangstenboek/?utm_source=learning_center&utm_medium=referral

and perhaps you also have a cash book?
https://dexxter.be/wat-is-een-kasboek-moet-je-dit-bijhouden/?utm_source=learning_center&utm_medium=referral

OK, but sometimes I have more than 18 patients in a day. I will definitely exceed the stated 250 euros. I would then have to create a new line each time, which I find too complex...

The €250 mentioned is per person.
https://www.youtube.com/watch?v=ut2NvU94dQg

OK, so can I put the group of patients who came in for treatment under one line (which is then higher than 250 EUR)?

Yes, like the example of the 10 items from 30 EUR in the video.